A flow-rate controller for controlling the flow rate of a fluid is constituted of a plurality of components, such as a flow meter and a flow-rate control valve. An example of such a known flow-rate controller is a flow-rate control system described in Patent Document 1, mentioned below. The components used in a flow-rate controller include, for example, a Karman vortex ultrasound flow meter, described in Patent Document 2 mentioned below, including a plurality of components and a differential-flow meter directly connected to piping, described in Patent Document 3 mentioned below, that has an integrated structure.
There is a desire for reducing the footprint of devices that use flow-rate controllers, and in association therewith, there has been an increasing desire for reducing the size of various pipe members.
Since the devices are presumed to be used for a long period of time, ease of maintenance is also desired by customers. Therefore, inevitably, there has been a desire for improving the ease of maintenance of flow-rate controllers used in such devices.
A flow-rate controller is required to be able to stabilize a specific flow to a target flow-rate value even when there is a fluctuation in pressure and flow rate on the primary and secondary sides of the valve. Moreover, when there is a change in the target flow rate, the flow-rate controller must be able to immediately respond.(See Japanese Unexamined Patent Application, Publication No. HEI-9-303609; Japanese Unexamined Patent Application, Publication No. 200-186950; Japanese Unexamined Utility Model Application, Publication No. HEI-02-55123.)